The major objectives of the proposed research are 1) to determine the role of the arterial baroreflexes and the cardiopulmonary mechanoreflexes in mediating the resistance changes that occur in individual vascular beds during exercise and 2) to examine the phenomenon of "sympatholysis" of exercise in conscious dogs. Recent evidence indicates that acute interruption of the arterial baroreflexes results in an abnormal blood pressure response during exercise despite a normal cardiac output response; this suggests arterial baroreflexes contribute to blood pressure regulation during exercise via changes in total systemic vascular resistance. Similarly, acute interruption of cardiopulmonary reflexes in chronically sinoaortic denervated dogs results in a post-exercise elevation in arterial pressure which occurs as a result of an elevated total systemic vascular resistance. This project will examine the regional vascular resistance changes that occur during exercise and recovery in the presence and absence of arterial baroreflexes and cardiopulmonary mechanoreflexes. Arterial baroreflexes will be interrupted in two ways: 1) chronic interruption will be accomplished by surgical sinoaortic denervation and 2) acute interruption will be accomplished by vascular isolation and pressurization of the carotid sinuses in conscious aortic denervated dogs. Interruption of cardiopulmonary reflexes will be accomplished through bilateral cervical vagus nerve section. Blood flow will be recorded and resistance calculated for the celiac, internal iliac, renal and superior mesenteric vascular beds. Mean arterial pressure, cardiac output and heart rate will also be continuously recorded during twelve minutes of mild or progressive exercise. "Sympatholysis" of exercise refers to the reduced ability of resistance vessels in exercising muscle to constrict during sympathetic stimulation. However, this phenomenon has only been described in anesthetized animals using simulated exercise. This project will examine the effect of reflexly increasing sympathetic tone to resistance vessels in skeletal muscle during exercise in conscious dogs. This will be accomplished by suddenly reducing carotid sinus pressure to 40 mmHg at various times during exercise; iliac resistance will be calculated to determine the effectiveness of sympathetic stimulation. Results from this research will make a significant contribution to our understanding of the complex mechanisms involved in the regulation of arterial blood pressure, unencumbered by anesthesia or surgical trauma.